The Measurement And Numeric Analysis Of Millisecond Laser Induced Damage Of Optical Coatings Components

Optical coating is one of the most important and frangible components in optical systems. The millisecond laser induced damage of optical coatings and the damage mechanisms are studied through theoretical studies, numerical analysis and experimental researches. The characteristics of millisecond laser induced damage are also explained.The impacts of the field distribution on the coatings under the radiation of millisecond laser are studied. The electric field distributions are calculated by the Maxwell Equations, and the physical model of the optical coatings radiated by millisecond laser is established according to the heat conduction equation and the finite element method, afterward, the temperature and the stress fields are calculated. The results show that the thermal conduction weakens the impact on the temperature distribution induced by the electric field distributions. The existence of the standing wave in the coatings will not reduce the millisecond laser induced damage threshold greatly.The physical model of the optical coatings with defects radiated by millisecond laser is established. The temperature fields are calculated under the conditions of a series of defect radius and depth according to the model with defects. The results show that the defects in the coatings reduce the damage threshold, and the coatings are prone to be damaged by large defect radius and high electric field.The characters of two kinds of typical coatings are investigated. The damage thresholds of the two kinds of coatings are studied according to iso-11254, and the damage morphologies are also observed and analyzed by optical microscope. The characters of coatings with single layers at different thickness are also studied.The damages of optical coatings induced by large energy density millisecond laser are investigated. Millisecond large energy laser not only damages the films but also destroys the substrate of the coatings, and then forms a cone shaped cavity on the substrate. The depth and the radius of the cavity vary with the energy density of the laser. The research results show that the cone shaped cavity is tend to be steady while the energy density of the laser reaches 2×104J/cm2, as the steam of the matter in the radiation area absorbs part of the energy of the laser.The damage of coatings induced by laser at 10ns and 1ms are investigated. The damage threshold and the damage morphologies are also studied. The results of lms laser induced damage of coatings show that the damage is induced by the defects and the damage depth is about 200μm. The results of 10ns laser induced damage of coatings show that the damage is induced by cumulative ionization and the damage depth is about 102nm scale. And then, a physical model of coatings without defects and impurities radiated by a series of pulse durations is established to study the temperature fields of the coatings. Calculated results show that the area and depth of the damage induced by 1ms laser are larger and deeper than those by the short pulse one.These research results in the paper will not only deepen the understanding of millisecond laser induced damage of optical coatings, not also improve the cognition of the damage mechanism. At the same time, it would provide the theoretical and experimental foundations for the research of anti millisecond laser coatings.